This invention relates to the production of glass fibers, e.g., fibers made by melting particulate batch ingredients or minerals, including basalt and the like, and, more particularly, to a method of and apparatus for detecting the level of molten glass in a glass melting furnace.
In the production of glass, it is desirable to maintain a substantially constant head or level of molten glass in the melting furnace to reduce the erosion of the refractory and to provide a constant glass feed to the bushings. The prior art has employed bubbler systems, such as those disclosed in Tretheway, U.S. Pat. No. 3,200,971, to detect the level of molten glass in the furnace. However, such systems are not suitable for electric furnaces that have a layer of batch material on the surface of the molten glass, because the bubbles may disturb the batch layer and/or become trapped beneath the bottom of the batch layer and the top surface of the molten glass thereby making the dividing line therebetween indistinct.
Canfield et al., U.S. Pat. No. 4,194,077, provides a method of approximating the level of molten glass in the furnace by measuring the thickness of the batch layer and then subtracting the batch thickness from the level of the batch layer in the tank. However, such method does not directly measure the level of the glass. An ultrasonic sensor detects the level of the batch layer, and a bubbler system detects the level of molten glass in the forehearth of the furnace; this data is then incorporated along with the density of the glass and density of the batch into a formula to calculate the thickness of the batch layer. This thickness is then subtracted from the level of the batch layer detected by the ultrasonic sensor to provide an approximation of the level of molten glass in the furnace.
Therefore, it is an object of the present invention to provide a method of and apparatus for directly detecting the level of molten glass in a furnace having a layer of batch material on the surface of the molten glass.